Ions that travel through space create a magnetic field. Using the right hand rule, we can determine the direction of the magnetic field lines.
When 2 particles travel in the same direction, their magnetic field lines are oriented in the same direction and will therefore combine. Electrons will be pulled from the particle with the lowest magnetic field to the particle with the higher magnetic field. Electron velocity will increase as they travel from particle 1 to particle 2 and so on.
Objects in the spiral arms of a galaxy closest to the center will move slower than objects in the periphery of the spiral arms. The difference in magnetic fields will cause electrons to flow from the center to the periphery.
